This article was researched and written by a student at Texas Tech University participating in the Encyclopedia of Earth's (EoE) Student Science Communication Project. The project encourages students in undergraduate and graduate programs to write about timely scientific issues under close faculty guidance. All articles have been reviewed by internal EoE editors, and by independent experts on each topic.

Introduction

The Rio Grande River flows from its headwaters in the San Juan Mountains of southern Colorado to the Gulf of Mexico near Brownsville, Texas. Also known as the Rio Bravo in Mexico, the river forms a natural boundary between the United States and Mexico. Because the river flows primarily through arid regions, the water in the Rio Grande River is important for human consumption, agriculture, and as a water source for wildlife. In addition, dams along the river provide for hydroelectric power and recreation.

History

Rio Grande River Basin. (Source: World Wildlife Fund)The Rio Grande has been used as a water source for a number of Native America tribes along its length. Álvar Núñez Cabeza de Vaca (1535 or 1536) and Francisco Vázquez de Coronado (1540) are two of the first Europeans to experience and explore the river. The river was not well mapped until it became the international boundary between the United States and Mexico following the Treaty of Guadalupe Hidalgo in 1848.

Facts and figures

The Rio Grande begins as a clear spring and snow-fed mountain stream 12,000 feet above sea level in the Rio Grande National Forest, San Juan County, Colorado. It originates at the Continental Divide in the San Juan Mountains and cuts through the middle of New Mexico to El Paso, Texas. At that point, the river begins as the international boundary, and it forms the western or southern border of the Texas counties of El Paso, Hudspeth, Presidio, Brewster, Terrell, Val Verde, Kenney, Maverick, Webb, Zapata, Starr, Hidalgo, and Cameron. The river’s length from its headwaters to the Gulf of Mexico varies as its course changes, but in the late 1980s the International Boundary and Water Commission stated the total length to be 1,896 miles. The official border length is in the range of 889 to 1,248 miles depending on how it is measured.

Depending on how it is measured, the Rio Grande is the twenty-second longest river in the world and the fourth or fifth longest in North America. It drains more than 40,000 square miles in Texas alone. The river’s main tributaries are the Pecos River, the Devil's River, the Chama River, and Puerco Rivers in the United States, and the Rio Conchos, Rio Salado, and Rio San Juan in Mexico. The Rio Grande, however, is in a sense two streams. At Presidio, the river dwindles to nearly nothing, and only water from Rio Conchos continues the journey down to the Gulf.

Contrary to its name, the Rio Grande is not large enough to be navigable at all by oceangoing ships or smaller craft. It is barely navigable at all and is limited to canoes, rafts, and in some areas personal watercraft. The river’s natural flow is only 1/20 the volume of the Colorado River and less than 1/100 that of the Mississippi River.

Agriculture

Agriculture and cattle raising are the leading industries around the Rio Grande, and the crops grown vary along the river. In Colorado and northern New Mexico the major crops are potatoes and alfalfa whereas major crops in southern New Mexico and West Texas include cotton, peppers, onions, and pecans. Farmers in the lower Rio Grande Valley raise citrus fruits, vegetables and cotton. The river, aided by dams, is used to irrigate many of these crops. Sixty thousand acre-feet of irrigation water is annually promised to Mexican farmers in the Juarez area, although this number is proportionally decreased during times of low snow melt-off in Colorado.

Major Cities

Rio Grande River flowing though El Paso. (Source: University of Texas, El Paso)The major cities and towns alongside the Rio Grande are Santa Fe, Albuquerque, Socorro, Truth or Consequences, Mesilla, and Las Cruces in New Mexico; and El Paso, Presidio, Del Rio, Eagle Pass, Laredo, Rio Grande City, McAllen, and Brownsville in Texas. On the Mexican side the primary towns and cities are Ciudad Juarez, Ojinaga, Ciudad Acuna, Piedras Negras, Nuevo Laredo, Camargo, Reynosa, and Matamoros. These are located in the Mexican states of Chihuahua, Coahuila, Nuevo Leon, and Tamaulipas. Ciudad Juarez, in 1980, was the largest city on the Rio Grande, and El Paso was the second largest city on the border. Together, the two cities would constitute one of the world’s major metropolitan areas if the Rio Grande did not divide them.

Dams

Today, dams along the Rio Grande are used for irrigation, flood control, and regulation of the river flow. Elephant Butte Dam, completed in 1916, and Caballo Dam, completed in 1938, in New Mexico create reservoirs that serve large areas. These were built to provide a steady supply of irrigation water on demand. Downstream about 12 miles northwest of Del Rio, Texas, the Amistad Dam, completed in 1969, is 6 miles long and impounds a huge reservoir. Further on just below Laredo, Falcon Dam, completed in 1954, creates another large reservoir.

Issues

Endangered speciesThe Rio Grande silvery minnow (Hybognathus amarus) historically occupied approximately 2,400 river miles in New Mexico and Texas. In 1994, the silvery minnow were classified as endangered in the U.S. by the standards set forth in the Endangered Species Act of 1973. The species used to be found in the Rio Grande from Espanola, New Mexico, down through Texas to the Gulf of Mexico. Currently, the silvery minnow is believed to live only in one reach of the river in New Mexico, a 174-mile stretch that runs from Cochiti Dam to the Elephant Butte Reservoir. This current habitat is about 7% of its former range.

International boundaryUsing a river as a natural international border is helpful since the boundary is easily distinguished, but it has its faults as well. A meandering river such as the Rio Grande is constantly changing, eroding away one bank and depositing on the other. Long brushy curves shaped like horseshoes or oxbows frequently overflow and form new channels. This movement complicates defining the exact international border. Sections along the Rio Grande have been straightened to help prevent the erosion and deposition of sediments. One in particular is the canalization of the river section separating El Paso from Juarez. Today, the border runs down the middle of the deepest portion of the river.

Invasive speciesInvasive species of plants along the banks of the Rio Grande are also becoming an environmental issue. Plants such as tamarisk (Tamarix sp.) and giant cane (Arundinaria gigantea) are outcompeting native species and replacing them along the banks of the river, thus greatly altering the riparian zone. These plants extend their roots into the water supply and are accredited increasing the amount the water loss from the river.

Recreation

In a remote stretch in west Texas, the Rio Grande makes a curve to the northeast to form the “big bend.” It is here that outdoor enthusiasts can enjoy themselves in the Big Bend National Park. A 191.2 mile section of the river on the American bank is designated as the Rio Grande Wild and Scenic River. It begins in Big Bend National Park and runs down to the Terrell-Val Verde county line. The designation of a Wild and Scenic River is only given to 2% of all the rivers in the United States for being free flowing and pristine.

Recreation along the Rio Grande. (Photo by Alicia Freitag)The Big Bend area is administered by the U.S. National Park Service, though there are no federal facilities. The area had 525 daily visits and 4,329 overnight stays in 1990. The Wild and Scenic River is divided into 3 sections commonly used for canoing:

Mariscal Canyon – A 10 mile, one day trip beginning at Talley and ending at Solis Landing. The canyon itself is six miles long with walls exceeding 1,400 feet.

Boquillas Canyon – A 33 mile, two to three day trip beginning at Rio Grande Village and ending at Heath Canyon, Texas (downstream from La Linda, Mexico). Boquillas Canyon is the longest canyon trip in Big Bend National Park, and its wall rise 1,200 feet.

The Lower Canyons – A five to ten day trip beginning at Heath Canyon and ending at either Dryden Crossing (83 miles) or Foster’s Ranch (119 miles), which is at the end of the Rio Grande Wild and Scenic River.

2. Here is a link to an article on the Rio Grande River in the Handbook of Texas Online - http://www.tshaonline.org/handbook/online/articles/RR/rnr5.html

3. There is a youtube video entitled - Rio Grande- Natural HistoryIt is a little bit hokey (I didn't know that you could make a video by simply lecturing over your powerpoint slides with Native American music in the background- I wish I had one of those cool "announcer voices"). It does have good information about the path of the river so you should take a look. Unfortunately, I wasn't able to figure out how to let you view the video online. thus, to find it Google "Rio Grande River" and click on "Videos" and look for the video entitled Rio Grande - Natural History.

By the end of this course the fully engaged student should be able to- locate the Rio Grande River on a map- roughly draw the location of the Rio Grande drainage basin on a map- list some tributaries of the Rio Grande in Mexico and the USA- identify the source of the Rio Grande- discuss the variety of ecosystems that the Rio Grande flows through- explain why the Rio Grande River primarily flows through arid regions